The -10 mnd really doesn't matter a whole lot. Despite what the poster below has said, mnd affects magic resistance against white magic, not black magic spells. That's affected by int.
But it's really a moot point - instead of spending your sky points and hard-earned gil getting these, just do Mamool Ja assaults and get the Amir boots. Much sexier and no -mnd penalty.
I just wish I'd noticed the Amir boots before getting these. Ah well :/
[and btw if you do use them - just macro them out for mnd-based WS].
-Calea